June 26, 2014
Here’s a topic that I get asked about more than any other: “How do you get those weaved welds?” These days I rarely (occasionally, but not often) encounter the need to weave, but it’s fun, it looks rad, and it’s nice to stay sharp.
DISCLAIMER: I'm not a boilermaker, and I'm not a pipe welder. Those guys, the ones that do this day in and day out, are the masters. I'm not the end-all, be-all expert on the subject. But I get asked enough about certain aspects of it that I'll share some of what I've learned and figured out over the years.
There are basically two ways to weave a TIG weld: walking the cup and freehand. We’ll hit on the latter in a bit, but right now let’s focus on the former.
Most people assume that all weaved TIG welds are “walked.” It’s by far the more popular method, and for good reason. Walking is the go-to technique for TIG pipe welding, and not because it looks cool; it’s a fast and efficient way to dump a bunch of filler into a joint with a TIG torch.
To start with, it's ideal for joining an open-root V-groove (Figure 1). Everyone has their own style, and everyone sets up their joints a little differently, so this description will be a little generic.
For the root, I like to use a cup sized so that it sits just inside the groove (Figure 2; See slideshow for this and other figures). I have the tip of the tungsten just above the root opening, and I lay wire. I try to use a filler rod that's big enough to sit above the lands without falling through the root, and I melt it in as I move the cup forward by rocking it side to side.
You want to keep the arc focused in the root area (basically land to land) so you get penetration into both toe lines on the backside. You can move quickly, and you'll get a bead that's perfect on the back of the joint as well as the face.
I don't actually get asked about that part too often, but I wanted to put it out there because it's critical. It's the way to weld an open-root pass.
Most of the questions I get are about the cover passes (both on V-grooves and fillets). You know ... cuz a weave cover looks cool. Do I pulse the pedal or keep the amps steady? Do I lay wire or dip the filler? Am I walking the cup or freehanding the torch? Well, the answer to all three questions could be yes. There is no one way, no “right” way.
Walking a cover pass on pipe, to get it to look nice, flat, symmetrical, and clean, is the most difficult weld for me (Figures 3a and 3b). But it’s also one of the most rewarding. You're constantly changing the angle of both the filler and the torch. Unlike a V-groove or a fillet joint, where you have two surfaces that act as a guide, there is only one surface to rest the cup on. Because of this, you're using the front edge of the cup as a fulcrum.
Balance can be difficult to the point that some welders will freehand the cover weave or run stringers, as opposed to walking the cup. The root and the filler passes on pipe are pretty much cake, so for cover practice I'll sometimes just take a pipe and scribe a couple of lines to simulate the groove edges. It's actually more difficult because there is no groove or physical edge for the filler to flow into, so it's very helpful for practicing puddle control.
Laying the wire, while also giving it a slight push into the puddle to maintain the weld bead’s profile/size, usually is the best way to attack the cover pass on pipe. Sometimes I roll the wire with the cup and puddle, other times I dip the filler from side to side. You can mess around with different sizes of rod, or even doubling the rod up as well.
On the pass before the cover on a V-groove, I get as close to the edges of the groove without burning them out and as flush to the surface of the pipe without going over. This gives you the ability to build a nice, even, just-above-flush cover on the last pass.
On the fillets, I typically run a root pass first. You can still walk it, but it will be a smaller, narrower bead penetrating where the two pieces of metal come together (Figures 4a and 4b).
Usually on the root pass I lay the rod; the trick is to keep it on the leading edge of the puddle. If you pull it away even a bit too far, the tip of the rod may ball up instead of wetting into the weld pool. If you're pushing it into the puddle, you'll create a larger bead that will be too concave or won't penetrate enough. You want to find a happy medium for a consistently sized weld that digs into the base material.
For the passes after the root, the technique you use is what affects the appearance of the bead. Remember that the pattern of the weld is caused by the way the puddle "freezes." Different things affect the temperature of the puddle. Amp input is the obvious one, but another, less obvious factor is that adding filler sucks away heat. If you're dipping the rod, there's a more noticeable ripple than if you're laying wire, because there is the slightest bit of temperature change with each dip. Speed and material thickness can also have an effect (Figures 5a and 5b).
The welds in Figures 5a and 5b were done walking the cup. Sometimes that isn't an option, whether it's because of space constraints or because the procedure won't allow the cup to touch the work. In those cases, it's good to be able to do a freehand weave as well. It's possible to get welds that look just as consistent as you get from walking, but it's definitely not as easy. Actually, the concept of doing it freehand is probably easier; you're just doing the motions with your hands, fingers, and wrist; there's no need for balancing and leveraging your cup on the material. The execution, however, is a bit more difficult to do, at least to achieve consistent results (Figures 6a and 6b).
I remember seeing a pipe section that was on display in one of my first welding classes at the UAW/Chrysler training center. It had been TIG welded by a guy who placed in the top 5 of a world welding competition. He walked the cup all the way around. Instructors described him as a machine. I wanted to duplicate that pipe, and then be better than that pipe.
I remember seeing a picture of a weld Jesse James did on a hot rod frame with a freehand weave pattern, and I worked to see how I could emulate that. I'd see welds that pipefitters would post of their nuke cert welds, and I'd try to discover their technique.
Often I'll find something that works while I'm just laying beads and practicing, and then I'll fine-tune it. Nothing beats inspiration and hood time. There are a lot of different styles and techniques out there waiting for you to take them on.
Practice doesn't make perfect, but it's the only way to reach your ceiling.